1. Field of the Invention
The present invention relates to a system and method for controlling an engine idling speed applicable to an internal combustion engine in which the engine idling speed, at a time immediately after a disturbance (external load) occurs, is stabilized.
2. Description of the Background Art
A Japanese Utility Model Registration First Publication No. Heisei 1-158537 exemplifies a previously proposed engine idling speed control system.
In the above-identified Japanese Utility Model Registration First Publication, an idling control valve is installed in a bypass passage bypassing a throttle valve. The throttle valve serves to open and close an intake air passage of the engine.
The engine idling speed is thus controlled by adjusting the intake air quantity passing through the bypass passage by means of the idling control valve to which a pulse signal having a pulse duty factor (ratio) is supplied.
The pulse duty ratio is set according to a basic controlled value ISCT and a feedback correction value ISCI. The basic controlled value ISCT is set according to an engine coolant temperature. The feedback correction value includes a proportional constant ISCP and an integration constant ISCI.
Engine idling speed generally drops at high speeds when an relatively large external load is imposed, such as when a powered steering system, defogger, or air conditioner is operated.
If the drop in the engine idling speed is corrected via feedback control, hunting of the engine revolution speed occurs.
That is to say, since an increase rate of the integration constant ISCI is slow, the proportional constant ISCP fluctuates until the integration constant ISCI is settled to an appropriate value after the external load is added. Thus, hunting of the engine revolution speed N occurs.